Process for the production of diazotype copies



PROCESS FOR THE PRODUCTION OF DIAZOTYPE COPIES Application September 10, 1952, Serial No. 308,938

Claims priority, application Netherlands September 19,1951

2 Claims. (CI. 96-49) No Drawing.

The invention relates to a process for the production of diazotype copies by selective exposure (i. e. exposure to light of locally differentiated intensity) of one-component diazo film layers sensitized with a para-tertiaryaminobenzene-diazo compound and suitable for development with a liquid, and subsequent development with a developer containing an azo coupling component.

The development referred to above can take place in the known manner by immersion in .a bath of a developer or according to the thin-layer method (the so-called semi-wet development). The latter method is in practice generally carried out mechanically. These methods of development of diazotype copies are usually applied when the diazo layer is of the one-component type, i. e. does not contain any azo coupling component; the developer (diazotype developer) then contains, in addition to buffer salts, one or more azo components which have to cause the formation of the azodyestuifs.

In this type of diazotype printing use is preferably made of diazo compounds and azo coupling components with a fairly high coupling activity, unless it is desired to use strongly alkaline developers, which is often inadvisable. One may naturally use diazo compounds of slightly less coupling activity in combination with a very active azo coupling component and, conversely, combine a diazo compound of more coupling activity with an azodyestuff component of less coupling activity;

The azodyestuffs formed should not bleed in the developer.

Substances which in general have sufficient coupling activity for the practical application of the thin-layer development include: p diazo diphenylamine, p-diazoethyl-benzyl-aniline, p -diazo-di-normal-butylaniline, pdiazo-ortho-chloro-diethylaniline, the p-diazo 2.5 dialkoxy-acylanilides, and many others. The p-diazo-2.5- dialkoxyacyl anilides are very active, and even suitable for development at a pH in the vicinity of 7.

Examples of diazo compounds which in practice are preferably not used for diazotype printing with thin-layer development, in view of insufiicient coupling activity, are: p-diazo-aniline, p-diazo-monomethylaniline, p-diazo-dimethylaniline and also p-diazo-diethylaniline. P-

Statcs Patent ice diazo-dipropylaniline is on the borderline for the practical application of the thin-layer development.

As azo coupling-components having sufiicient coupling activity for the thin-layer development there may be mentioned: beta-naphthol, phloroglucinol, reso-rcinol, phenyl-lmethyl-3-pyrazolone-5 (very active), aceto acetic anilide; azo coupling components with insufiicient coupling activity are: phenol and 2.B-dihydroxynaphthalene- 6-sulphonic acid.

The term diazo film layer ishere used for a special type of diazo layer. In fact, the term diazo layer is Patented May 14, 1957 also used when the diazo compound is simply spread out on the fibres of a paper surface as a dried-up coating, perhaps in the form of a very thin uneven crust or a multitude of crusts. better-in contrast with common usageto speak of a zone instead of a layer proper. A diazo film layer does have the character of a true layer; in this case one may, for example, speak of thickness. It is obvious that a diazo film layer need not be equally thick throughout; it might, for example, show a relief. Such a diazo film layer is formed of matereial which is to be referred to hereinafter as film-forming material.

The diazo film layers have to be resistant to the treatment with the thin layer of the aqueous developer. In view of this, such diazo film layers must not be formed of film-forming matereial which presents serious difliculties when treated with an aqueous liquid, for example merging, dissolving, becoming objectionably sticky, and the like, as is the case with layers of gum, alkyl cellulose, soft gelatine, and similar substances. They must, however, be capable of readily accepting and absorbing the thin layer of developer; otherwise they are not suited for the thin-layer development either.

The diazo film layer will usually be mounted on a support; in special cases it may, however, also be independent.

It resulted from an examination that through exposure of various p tertiaryaminobenzene-diazo compounds there are formed certain products (hereinafter to be called photochemical decomposition products) which are capable of acting at room temperature on aqueous solutions of diazo compounds with a pH of over 7, whereas the photochemical decomposition products of other ptertiary-aminobenzene-diazo compounds do not have this effect, or only slightly so. The saidaction, if it takes place at all, proceeds more rapidly according as the pH of the solution is higher; it is very clear, for example, in the pH range of 9 to 10.

If it is to be possible for the action of the photochemical decomposition products of the various p-tertiaryaminobenzene-diazo compounds to be compared, it should preferably be tested with regard to a compound of this class which itself undergoes only very slight changes if any, when stored under the circumstances described. It was found that p-diethyl-aminobenzene-diazonium chloride met this requirement. If a 0.002 normal solution of the latter compound in water, to which sodium carbonate has been added to a pH of 9.5, is left to stand for 15 minutes at 18 C. (without exposure), the content of diazo compound in this solution has not altered to any measurable extent; the decrease of the diazo content was found to be about 2%. This is the blank test.

The action of the photochemical decomposition products of other p-tertiary-aminobenzene-diazo compounds is now tested by adding the photochemical decomposition product of the p-tertiary-aminobenzene-diazo compound to be tested to a similar solution as in the blank test. In order to obtain comparable results, the test is carried out in the following manner:

A weakly acidic 0.004 normal solution of the diazonium compound in question is taken and exposed to light until all the diazo compound has been decomposed. The liquid obtained is mixed with an equal volume of 0.004 normal p-diethylaminobenzene-diazonium chloride solution, and brought to a pH of 9.5 through addition of sodium carbonate. The mixture is now left to stand for 15 minutes at 18 C., after which the quantity of p-diethylaminobenzene-diazonium compound left behind is determined.

Under thecircum stances sketched above, the photochemical decomposition products; of thefollowing diazo In this case it would perhaps be compounds produced in the test solution a decomposition as stated behind the particular diazo compound:

From the above it is evident that there are practically inactive, slightly active, and very active photochemical decomposition products, in the sense defined above, of ptertiary-aminobenzene-diazo compounds. For the purpose of the invention the photochemical decomposition products are called active when they reduce the diazo content by at least 50% under the circumstances of the test described.

It was found that under certain conditions it is pos sible to obtain important efiects in the reproduction of half tones by means of certain p-tertiary-aminobenzenediazo compounds the photochemical decomposition products of which are active in the above sense.

I The invention relates to the production of diazotype copies by selective exposure of one-component diazo film layers sensitized with a p-tertiary-aminobenzene-diazo compound and subsequent development with a developer containing an azo coupling component. According to the invention, use is made of a diazo film layer containing a p-tertiary-aminobenzene-diazo compound the amino group of which is substituted by residues having in total at least seven carbon atoms and which upon exposure in aqueous solution forms a product that is active, the diazo film layer is exposed and developed with a diazotype developer containing an azo coupling component of the formula:

in which X represents a hydroxyl group or a carboxylic acidamide radical without an aromatic radical in the amide group. The amide group, however, may be substituted by substituents such as amino, hydroxyl, alkyl, substituted alkyl, for example hydroxyalkyl or aminoalkyl, aralkyl. Double substitution is also possible. Aromatic substituents in the amide group render the azo coupling component less suitable, such compounds being only slightly soluble in the developer liquid, at all events if the latter does not contain free alkali; moreover they have a tendency of often spoiling the tone of the lighter areas of the picture and of badly penetrating into the diazo film layer. The eifect obtained with this process consists in that the images thus obtained in the diazo film reproduce some half tones, specifically those in the dark areas of the image, in a richer gradation than is generally the case when other azo coupling components (for example the azo coupling components frequently used in diazotype printing with liquid development: phloroglucinol, phenyl-methylpyrazolone, resorcinol, and beta-naphthol) are used in the diazotype developer. The effect obtained in the process according to the invention is also greater than with the use of para-tertiary-aminobenzene-diazo compounds the photochemical decomposition products of which are inactive in the above sense, even when the azo coupling components prescribed for the invention are used. For mixtures of diazo compounds having active light decomposition products the same applies mutatis mntandis.

Particularly 'good results are obtained when the process awaeos 4 according to the invention is applied to diazo film layers containing diazo compounds of the general formula:

in which X is an anion, while R1 and R2 are alkyl radicals having together 10, 11 or 12 C atoms, each alkyl radical containing at least 4 and at most 7 C atoms, and not more than one of the two having a side chain attached to the alpha C atom.

For the production of diapositives and cinematographic films the diazo film layer is mounted on a clear film-shaped support. In this form the invention constitutes contribution to the application of diazotype printing for these purposes. Particularly strong images with good gradations in the dark half tones are obtained when the diazo content of the diazo film layer is between 0.8 and 2.0 millimols per m.

For the film-forming material for the diazo film layer it is advantageous to choose a hydrolysed cellulose ester with an average number of acyl groups attached to the OH groups between 0 and 1.5 (triacetate=3.0). Preferably a hydrolysed cellulose acetate is taken, but other esters, mixtures of esters or mixed esters, for example acetate-butyrates, are also very suitable. Particularly good results are obtained when the film-forming material of the diazo film layer consists of a cellulose ester with an acyl content increasing from the accessible side inwards, the portion of the layer that is insoluble in boiling dry acetone being at least 3 g. and at most 15 g. per m One may, however, also use other-more or less hydrophilic-materials, 'for example partially hydrolysed polyvlnyl esters, cellulose film (cellulose hydrate) mounted on a support, for the diazo film layer.

The use of gelatine as film-forming material may involve some ditficulties. Gelatine is a not very reliable initial material, and one type may behave differently from another. This behaviour may also be determined by the nature of the diazo compound of the diazo-gelatine layer. I n some cases the exposure is attended with the appearance of a so-called nitrogen screen, in other cases the lightsensitivity is smaller when a given combination of gelatine and diazo compound is used, in other cases again the thin-layer development proceeds slowly, etc.

An azo coupling component with which particularly good results are obtained is the hydroxyethylamide of 2-hydroxy-3-naphthoic acid. This produces blue images with a particularly good reproduction of the half tones on the diazo film layers with para-tertiary-aminobenzenediazo compounds according to the invention. For the production of images in more neutral tints, which also reproduce the half tones particularly well, it is of advantage to use in the developer a mixture of the betahydroxyethylamide of 2-hydroxy-3-naphthoic acid and a component influencing the shade (hue), the latter component preferably being the monomethyl ether or a monoester of resorcinol or its sodium salt (phenolate).

In another particularly good embodiment of the process according to the invention use is made of a diazotype developer with an azo coupling component according to the invention and an alkaline bufier mainly consisting of a borate, preferably potassium borate. Such a borate buffer may be composed of potassium metaborate and potassium tetraborate or of potassium tetraborate and potassium hydroxide. It is of advantage to add to the said borate developers substances such as mannitol, sorbitol, and the like, in general aliphatic polyhydroxy compounds with two or more hydroxyl groups attached to neighbouring carbon atoms. Also the addition of a xanthine to the diazotype developers is .to be recommended in those cases where the azo coupling component does not dissolve readily. V

The use of amides of 2-hydroxy-3-naphthoic acid together with a xanthine in diazotype printing is known, as

is also the use of hydroxyalkyl amides of 2-hydroxy-3- naphthoic acid, of aminoalkyl amides of 2-hydroxy-3- naphthoic acid, and of dihydroxy-2.3-naphthalene and its derivatives. A process for obtaining a better reproduction of the half tones with diazo film layers, in which the images are developed with a diazo-type developer after an alkaline intermediate treatment, is described in the U. S. A. patent application No. 276,061, and the process according to the present invention is in many respects analogous to the latter; it avoids, however, the intermediate treatment.

Copies with the full half tone efiect possible according to the invention naturally are not always desirable. If copies with a reduced half tone effect are desired, in the diazo film layer a portion of the para-tertiary-aminobenzene-diazo compound that forms an active product upon exposure is replaced by an equivalent amount of a diazo compound that forms a less active or inactive product, and by the selection of given quantities of the two diazo compounds the reproduction of the half tones can thus be controlled. Preferably two diazo compounds with a fairly matched coupling activity are chosen. If the diazo compound replacing the diazo compound according to the invention forms an azodyestufr" of a different tint with the azo coupling component(s) used, its presence naturally affects the gradation of the ultimate image.

The use in the present process of diazo film layers with diazo compounds differing in the above sense is naturally covered by the invention.

Any desired reduction of the half tone effect can also be obtained by replacing in the developer a portion of the azo coupling component(s) according to the inven tion by equivalent amounts of azo coupling component (s) of greater coupling activity.

The following examples illustrate the invention. Wherever reference is made in these examples to good gradation or good reproduction of half tones, what is meant is: better gradation or reproduction of half tones than would have been obtained, if the azo coupling components, such as phloroglucinol, generally used for the liquid development of diazotype copies had been applied in the developers.

Example 1 acetic acid, averages about 20% (which corresponds to an average number of acetyl groups attached to the OH groups of about 0.7), is impregnated on the deacylated side of the cellulose acetate layer for 30 seconds with the following solution:

22 g. zinc chloride double salt of p-diazo-di-normalhexylaniline 3 g. citric acid 3 g. ammonium chloride 50 cm. ethyl alcohol (96%) 900 cm. water The excess of liquid is removed from the cellulose acetate surface, and the material is subsequently dried. It contains about 0.8 millimol of diazo compound per m After exposure under a diapositive, about g. per m. of the following developer is applied on the copy:

g. beta-hydroxynaphthoic acid-hydroxyethylamide g. thiourea 1 g. sodium salt of isopropylnaphthalene-sulphonic acid g. sodium carbonate 1000 cm. water.

A blue image with good gradation, particularly in the dark areas, is obtained. 7

If 5 g. resorcinolrnonomethylether or 2 g. resorcinolmonoacetate are added to the above developer, fine black images with approximately the same gradation are obtained. If the betahydroxy-naphthoic acid-hydroxyethylamide is replaced by 15 g. betahydroxy-naphthoic acid amide plus 30 g. cafieine, a violet image with good gradation is obtained.

Example 11 In Example I the p-diazo-di-n-hexylaniline is replaced by an equivalent amount of p-diazo-ethylbenzylaniline, and the development is effected, after exposure under a dia' positive, with a developer of the following composition:

16 g. beta-hydroxynaphthoic acid-carboxymethylamide 20 g. thiourea 1 g. sodium salt of isopropylnaphthalene-sulphonic acid 70 g. potassium tetraborate-pentahydrate 20 g. potassium carbonate 1000 cm. water An image in a blue tint with good reproduction of half tones is obtained.

If beta-hydroxynaphthoic acid-carboxymethylamide is replaced by an equivalent amount of beta-hydroxynaphthoic acid-aminoethylarnide, practically the same result is obtained.

Example III Paper of 210 g. per m. which is coated on one side with a cellulose acetate layer of 10 g. per m? with an acetyl content calculated as combined acetic acid of about 53% (corresponding to a number of acyl groups of about 2.3), is immersed on the lacquered side in a solution of:

60 g. partially hydrolysed polyvinyl acetate (Elv-anol 2.0- of Dupont, 47% hydrolysed, corresponding to a polyvinyl acetate content of 67%) 12 g. sodium salt of naphthalene-1.3.6-trisulphonic acid 5 g. Zinc chloride double salt of p-diazo-di-n-hexylaniline 650 cm. ethyl alcohol of 96% 350 cm. water,

and subsequently dried. The diazo-polyvinyl acetate layer of 3 g. per m? thus formed contains about 0.8 millimol of diazo compound per m.

After exposure under a diapositive, about 14 g. per m? of the developer of Example 11 are applied on the surface of the image, the beta-hydroxynaphthoic acidcarboxymethyl amide, however, being replaced by an equivalent amount of beta-hydroxynaphthoic acid-monoethanol amide. The reproduction of the half tones is good, particularly in the dark areas of the image obtained.

Example IV Baryta-coated paper of 170 g. per m? with a dull surface is dipped with its baryta-coated side in a solution of 15% polyvinyl acetate (with a softening point of about 130 C. and a molecular weight of about 60,000 according to osmotic determination) in methyl alcohol, and dried. Thus a hydrophobic layer of a thickness of about 5, is formed on the baryta-coated surface. It serves to prevent the penetration into the baryta layer of the diazo solution to be applied subsequently. On to this layer there are new cast about cm. per m. of a (colloidal) solution of 40 C. of:

25 g. cellulose acetate of an acetyl content corresponding to about 28% of combined acetic acid (corresponding to an average number of acyl groups attached to the OH groups of about 1.1)

2 g. zinc chloride double salt of p-diazo-di-normalhexylaniline 0.15 g. alum of potassium 500 cm. ethyl alcohol (96%) 500 cm. water The casting material is cooled to about 10 C., as a result of which it sets. It is then dried in an air current of about 50 C. The cellulose acetate film thus formed has 7 a' thicknessof about 3,uf The layer' contains about 0.7 millimol of .diazo compound per m9. After exposure under a diapositive there are applied on the surface of the image about 12 g. per m? of 'the following liquid: i

15 g. beta-hydroxynaphthoic acid-monoethanolamide 3 g. sodium salt of isopropylnaphthalene-sulphonic acid 3 g. sodium salt of the niono-ethyl-Z-hexyl-ester of sulphuric acid 1 g. potassium salt of hydroquinone-sulphonic acid 70 g. potassium tetraborate-pentahydrate 20 g. potassium carbonate 1000 cm. water A violet image with good reproduction of the half tones of the original is obtained.

Example V On to a cellulose acetate film of 140 g. per m? there is applied, through immersion at 30 C., a diazo film layer of the following composition:

90 g. gelatine (J05 of Hasselt Vilvorde) 2.75 g. zinc chloride double salt of p-diazo-di-n-hexyl aniline 0.2 g. tartaric acid 1000 cm. water.

The film layer, which after drying has a thickness of about contains about 1 millimol of diazo compound per m.

The film has a relatively low light-sensitivity. After exposure under a cinematographic film positive, 10 g. per 111. of the developer of Example III is applied on it. A positive cinematographic copy with good reproduction of the half tones is obtained.

Example VI The diazo film layer of Example I is developed, after exposure under a diapositive, by the application of 9 g. per m with a solution consisting of:

10 g. 2.3-dihydroxynaphthalene 20 g. thiourea 30 g. sodium carbonate 400 cm. alcohol 600 cm. water A fine blue image with good reproduction of the half tones is obtained.

Example VII Paper with a deacylated cellulose acetate layer as described in Example I is impregnated on the deacylated side of the cellulose acetate layer during 30 seconds with the following solution:

15.4 g. zinc chloride double salt of para-diazo-di-normalhexylaniline 7 g. zinc chloride double salt of diazo-l-benzoyl-amino- 4-diethoxy-2.5-benzene 3 g. citric acid 3 g. ammonium chloride 50 cm. ethyl alcohol (96%) 900 cm} water.

The excess of liquid is removed, and the material is dried.

After exposure under a diapositive the development is effected in the manner of Example I with the aid of a developer of the following composition:

g. beta-hydroxynaphthoic acid-hydroxyethylamide 10 g. caffeine g. thiourea 1 g. sodium salt of isopropylnaphthalene-sulphonic acid 30 g. sodium carbonate 1000 cm. water. i

' 8 r A blue image with'a gradation that is less soft than that of the image obtained in Example I is obtained.

Example VIII Paper is treated and sensitized according to Example I.

After exposure under a diapositive the development is efiected in the manner of Example I with a developer of the following composition:

15 g. beta-hydroxynaphthoic acid-hydroxyethylamide 4.5 g. resorcinol-monoethylether 3 g. phloroglucinol 10 g. caffeine 20 g. thiourea 1 g. sodium salt of isopropylnaphthalene-sulphonic acid 30 g. sodium carbonate 1000 cm. water.

A bluish-black image is obtained, with a gradation that is less soft than would have been obtained, if the phloroglucinol had been omitted from the developer.

What we claim is:

1. A process for the production of diazotype copies which comprises selectively exposing to light a one-component diazo film layer, the film-forming material of said film layer consisting of an at least partially hydrolyzed cellulose ester wherein the average number of acyl groups attached to OH groups is from 0 to 1.5 and containing a light-sensitive p-tertiary-aminobenzene diazo compound of which the amino group is substituted by hydrocarbon residues containing in total at least seven carbon atoms and which yields an active photochemical decomposition product in the sense that a quantity of the solution obtained upon totally decomposing by light all of said compound contained in a weakly acid 0.004 11 aqueous solution of said compound, when mixed with an equal quantity of a 0.004 11 aqueous solution of p-diethylamino benzene diazonium chloride, and allowed to stand at 18? C. and at a pH of about 9.5, decomposes at least half of the amount of diazonium chloride in the latter solution within 15 minutes, said diazo compound upon exposure being capable of reacting with its photochemical decomposition product under alkaline conditions with the efiect that the part of said diazo compound so reacted no longer will couple with an azo coupling component to give a dyestufi'; and thereafter developing the exposed diazo filrn layer by applying to it a diazotype developer containing an azo coupling component of the formula:

in which X is a radical selected from the group consisting of a hydroxyl and a carboxylic acid amide radical containing no aromatic radical attached to the amide nitrogen atom, whereby the aforesaid reaction between said diazo compound and its photochemical decomposition product is brought about at said certain areas of said layer and said azo coupling component couples with the remaining part of said diazo compound.

2. A process for the production of diazotype copies which comprises selectively exposing to light a one-component diazo film layer, the film-forming material of said film layer consisting of an at least partially hydrolyzed cellulose ester, the acyl content of said material increasing progressively from the accessible side of said diazo film layer toward the interior thereof, said diazo film layer comprising from 3 to 15 grams of hydrolyzed matter insoluble in boiling dry acetone per square meter of said layer, and containing a light-sensitive p-tertiary-aminobenzene diazo compound of which the amino group is substituted by hydrocarbon residues containing in total at least seven carbon atoms and which yields an active photochemical decomposition product in the sense that a quantity of the solution obtained upon totally decomposing by light all of said compound contained in a weakly acid 0.004 11 aqueous solution of said compound, when mixed with an equal quantity of a 0.004 11 aqueous solution of p-diethylamino benzene diazonium chloride, and allowed to stand at 18 C. and at a pH of about 9.5, decomposes at least half of the amount of diazonium chloride in the latter solution within 15 minutes, said diazo compound upon exposure being capable of reacting with its photochemical decomposition product under alkaline conditions with the efiect that the part of said diazo compound so reacted no longer will couple with an azo coupling component to give a dyestufi'; and thereafter developing the exposed diazo film layer by applying to it a diazotype developer containing an azo coupling component of the formula:

ing of a hydroxyl and a carboxylic acid amide radical containing no aromatic radical attached to the amide nitro' gen atom, whereby the aforesaid reaction between said diazo com-pound and its photochemical decomposition product is brought about at said certain areas of said layer and said azo coupling component couples with the remaining part of said diazo compound.

References Cited in the file of this patent UNITED STATES PATENTS 2,037,542 Schmidt et al Apr. 14, 1936 2,233,038 Sus et a1. Feb. 25, 1941 2,241,104 Van der Grinten May 6, 1941 2,465,760 Sprung et a1. Mar. 29, 1949 2,528,460 Von Glahn et a1. Get. 31, 1950 2,541,178 Slifkin Feb. 13, 1951 2,542,716 Slifkin Feb. 20, 1951 2,616,803 Ravich Nov. 4, 1952 2,617,727 Slifkin Nov. 11, 1952 2,672,418 Neugebauer et al Mar. 16, 1954 FOREIGN PATENTS 337,868 Great Britain Nov. 13, 1930 

1. A PROCESS FOR THE PRODUCTION OF DIAZOTYPE COPIES WHICH COMPRISES SELECTIVELY EXPOSING TO LIGHT A ONE-COMPONENT DIAZO FILM LAYER, THE FILM-FORMING MATERIAL OF SAID FILM LAYER CONSISTING OF AN AT LEAST PARTIALLY HYDROLYZED CELLULOSE ESTER WHEREIN THE AVERAGE NUMBER OF ACYL GROUPS ATTACHED TO OH GROUPS IS FROM 0 TO 1.5 AND CONTAINING A LIGHT-SENSITIVE P-TERTIARY-AMINOBENZENE DIAZO COMPOUND OF WHICH THE AMINO GROUP IS SUBSTITUTED BY HYDROCARBON RESIDUES CONTAINING IN TOTAL AT LEAST SEVEN CARBON ATOMS AND WHICH YIELDS AN ACTIVE PHOTOCHEMICAL DECOMPOSTION PRODUCT IN THE SENSE THAT A QUANTITY OF THE SOLUTION OBTAINED UPON TOTALLY DECOMPOSING BY LIGHT ALL OF SAID COMTAINED UPON TOTALLY DECOMPOSING BY LIGHT ALL OF SAID COMTION OF SAID COMPOUND, WHEN MIXED WITH AN EQUAL QUANTITY OF A 0.004 N AQUEOUS SOLUTION OF P-DIETHYLAMINO BENZENE DIAZONIUM CHLORIDE, AND ALLOWED TO STAND AT 18*C. AND AT A PH OF ABOUT 9.5, DECOMPOSES AT LEAST HALF OF THE AMOUNT OF DIAZONIUM CHLORIDE IN THE LATTER SOLUTION WITHIN 15 MINUTES, SAID DIAZO COMPOOUND UPON EXPOSURE BEING CAPABLE OF REACTING WITH ITS PHOTOCHEMICAL DECOMPOSITION PRODUCT UNDER ALKALINE CONDITIONS WITH THE EFFECT THAT THE PART OF SAID DIAZO COMPOUND SO REACTED NO LONGER WILL COUPLE WITH AN AZO COUPLING COMPONENT TO GIVE A DYESTUFF; AND THEREAFTER DEVELOPING THE EXPOSED DIAZO FILM LAYER BY APPLYING TO IT A DIAZOTYPE DEVELOPER CONTAINING AN AZO COUPLING COMPONENT OF THE FORMULA: 